How to cut out the filter sock section of the sump on a Red Sea Reefer

[TexanReefer]

Not sure if this is the correct place to post, but I am trying to remove filter sock section of the Sump on my Red Sea Reefer 425xl. I have razor blades, but I am having trouble figuring out how to take out the black plastic filter sock portions. Can anyone give me some tips on how they did it?

Also should I put silicone down where the class meets the bottom of the tank?

 

[Futuretotm]

It’s all siliconed to each other pieces
I would run the blade everywhere
Technically only place you need to be careful is next to the seal of sump